This invention relates to door closers operating to automatically close an opened door, and more particularly to a door closer with hinge pieces in which a restoring coil spring is incorporated in hollow cylinders with hinge pieces over the entire length of the hollow cylinders.
In general, in a door closer of this type, the restoring torque of the restoring spring is reduced as the door opening degree is decreased when the door is closed, and it is necessary to allow a door locking means such as a latch to operate immediately before the door is completely closed. Accordingly, it is necessary that when the door opening degree becomes small the restoring torque is continuously applied to the door until the door locking means such as a latch is positively operated. Therefore, it is preferable that the door closer is so designed that even when the door is completely closed, that is, the door opening degree becomes zero, a present torque is applied to the door to a certain extent so that when the door opening degree becomes small, the present torque is added to the torque corresponding to that door opening degree.
In such a door closer, or in a conventional door closer constructed as shown in FIG. 1, a cylinder 103 having a support shaft 102 is fixedly fitted into a hollow cylinder 101 with a hinge piece 100', and the head section 104 of the cylinder 103 is protruded outside the cylinder 101. A hollow cylinder 105 with a hinge piece 100 is rotatably engaged with the head section 104. The support shaft 102 is surrounded by a coil spring 107 both end portions of which are secured to the head section 104 of the cylinder 103 and a cover 108 mounted on the hollow cylinder 105, respectively. The support shaft 102 is rotatably engaged with the cover 108. When, after the hinge piece of the hollow cylinder 101 is mounted on a fixing member such as a pillar and the hinge piece 100 of the hollow cylinder 105 is secured to a door, the door is opened, a restoring force is applied to the door by the elastic force of the coil spring 107. In this case, in general, a damper device having a hydraulic mechanism is separately provided so as to damp the restoring force.
In the above-described door closer, the hollow cylinder 101 is coupled to the hollow cylinder 105 through the head section 104 of the cylinder 103, and therefore the coil spring 107 utilizes only the limited internal space in the hollow cylinder 105. Accordingly, the length of the coil spring 107 employed in this limited internal space is necessarily short. It should be noted that the spring constant of a torsion coil spring is inversely proportional to the length thereof. Accordingly, in the conventional door closer, the spring constant of the coil spring is necessarily large. This means that as the door opening degree increases, the restoring torque is abruptly increased. If the door closer is so designed that with a large spring constant a great restoring force is obtained when the door opening degree is small, an extremely great restoring force is effected when the door is widely opened. This may obstruct the opening and closing operation of the door in practice. Thus, heretofore it is difficult to design the door closer so that a great restoring torque is effected when the door opening degree is small.
This difficulty may be overcome by decreasing the spring constant. Accordingly, it is a solution to this problem to increase the spring accommodating capacity as much as possible minimizing the number of components such as steel shafts or bearings giving a mechanical strength to the door closer. However, in this case, another problem pertaining to the durability attributed to a torsion stress with respect to the steel shafts is newly provided. This contradictory condition has not been overcome yet. Further, under the above-described conditions, we have frequently found that the door locking means such as a latch is not operated completely and positively when the door is closed.
The mounting of the door closer applied with the preset torque is carried out after the hinge pieces are opened, and therefore the preset torque is added to the restoring torque corresponding to the opening degree of the hinge pieces. Accordingly, the mounting of the door closer must be carried out while the hinge pieces is being opened with a considerably great force against the great torque which is the sum of the preset torque and the restoring torque. Accordingly, the door closer mounting work is rather troublesome and difficult; that is, it must be done by a skilled person with a great care. Thus, the conventional door closer suffers from a disadvantage that the work efficiency is very low. In addition, the solution to the problem of the aforementioned durability involves a new problem that the manufacturing cost of the door closer is increased.